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Solar Cells That Emit Light Break Efficiency Record
benfrog writes "Researchers at the University of California-Berkeley say they have come up with a counter-intuitive way of making solar cells more efficient — making them emit light. In a press release the scientists claim to be the first to demonstrate that the better solar cells are at emitting photons (the more LED-like they are), the more efficient they are at generating electricity. However, 'unlike an LED, the electrons in a solar cell are absorbing photons from an exterior source as well as emitting their own.'"
And polish them up.
Why don't they just funnel the emitted light back to the solar panels and thus make them independent of an external light source?
This would be great for space colonies and sea-floor dwellings.
Sounds like troll-physics.
Just like a good reflector of thermal energy also makes an excellent insulator, a good design for converting voltage to photons can be referenced to do the opposite.
If you've taken sophomore college physics, it's not counter-intuitive at all that an efficient absorber is also an efficient emitter.
[Sir Garlon] is the marvellest knight that is now living, for he destroyeth many good knights, for he goeth invisible.
Ideally, you would want all of your electron-hole pairs to never recombine (which would keep them from emitting photons). Since that's obviously not possible, this would be the best possible outcome of internal recombination.
Is this why plants fluoresce in near infrared?
Sure, it would be nice to have much more efficient solar cells, but there's another issue keeping costs up.
It's the home infrastructure.
Right now, it costs more to install the solar cells on a roof than it does to make them, and once you add in the cabling and battery/storage system for balancing the load or for nighttime use, the actual power generating part of the system is much less than half of the whole system cost. Increasing efficiency is great, and will let you cut the overall size of the system for a similar capacity, but the big issue is making a solar system that's easy to install, with cheap storage, for a lot less.
Cheap batteries and inexpensive support systems are the things we need now...
that the emitted photons could then be absorbed and converted to electricity by other light emitting solar cells?
Who else immediately thought of the solar powered car in the Logan's Run TV series? I could never understand why the solar collector glowed... now I know!
We heard you like light...
Why are these scientists wasting their time with so-called "solar cells"? Everyone knows solar energy can't possibly work. There's just not enough energy in the sun for it to be useful to us.
Fossil fuels are the result of plant life after millions of years, so they're the real "green" technology. And the sun had absolutely nothing to do with them.
These scientists, who are probably mostly foreign, want to strip us of our birthright: a personal vehicle that weight 6000 lbs. Hell, my wife, Lovey, has a couple of Escalades and she recycles all the plastic wrap that our food comes in. So who's really the "green" one?
You are welcome on my lawn.
Guess I can't tell that joke about a solar-powered flashlight anymore.
Haven't you heard? Roof mount solar cells are outdated 2-D tech. The new way is 3-D, made like branches and leaves on a tree. Much more efficient also. Instead of all sorts of equipment and manpower to roof mount, they will soon just send a truck with some "solar trees" and cement them in your backyard and run an extension cord to your house/batteries or to the meter to run it backwards. They look like trees from a distance so they are acceptable in more areas than ugly panels. Drill a hole, and put in the new tree. Quick, inexpensive, and more efficient.
Light emission is the converse of light absorption, so any solar cell that absorbs light must, by the same mechanism, emit light, unless other loss mechanisms prevent it. Obviously light emission is a loss mechanism-- light emitted is clearly not turned into electricity. However, all other loss mechanisms can be eliminated by sufficiently clever design, but light emission is a loss required by the laws of thermodynamics. Thus, a solar cell is optimized when there is no other loss mechanism other than light emission, which is to say, when the light emission is maximized.
(In fact, it is optimized when the light emission back toward the source is maximized; all emission that isn't back toward the source could in principle be retroreflected and reabsorbed. This would be known as "light trapping".)
http://www.geoffreylandis.com
some rolling roads, a life detector, and a massive fundamentalist revolution and we should be all set...
-- it's ridiculous how many people misspell ridiculous... (damn, damn, damn...)
Thermodynamics teaches us that the most efficient cyclical process is one that can be run in reverse the same way it is run forward. The more irreversible the process, the more it strays from equilibrium, the more it runs uncontrolled (all synonyms) the farther it is from being maximally efficient.
http://www.gizmag.com/nanocrystalline-silicon-nanoshell-photovoltaics/21391/
http://www.technologyreview.com/energy/39887/
Muchas Gracias, Señor Edward Snowden !
Silicon doesn't emit light because it is an indirect semiconductor. Because of that, it is also less efficient at absorbing light. That's why solar cells have to be so thick (several hundreds of microns), otherwise most photons would just go through the cell.
Direct semiconductors have been used in the past (e.g. GaAs) and they do achieve better efficiency. They are often used in space (they also happen to have wider band-gap, which is better suited to high energy photons, like ultraviolet light). GaAS cells are much thinner (a couple of microns) and lighter as almost all photons with energy above their band-gap are immediately absorbed.
Low cell thickness is good for efficiency - there is less chance that generated electrons will recombine. They simply have shorter distance to travel between the place they were generated at and an electrode. Also, the difference of the photon energy and the bandgap isn't simply converted into heat but rather another electron and is radiated back. It could be then captured by another narrow band-gap cell sandwiched with the main cell.
Perhaps they have found more reasons why direct semiconductors are more efficient, but it is not true that we didn't know it before.
Public roads, on public land are the essential infrastructure on which our society functions, it dates back long ago. It is done by the people (aka the government.) Everybody puts money in and everybody benefits.
The electrical grid gets heavy subsidizes and often leverages its monopoly power to corrupt government. The grid should be another public network just like the roads it usually runs next to. City water and sewage is also an old solution we continue. Electricity is now essential and while it is not as important as the traditional grids it is next in line to be made public. We should cast off these crooks who exploit our needs, corrupt our officials, and often poorly manage our power grid. It may cost us the same amount but we have 1 less source of corruption and an open grid to build a larger marketplace around. Private power grids are too cheap to think LONG term while government can build a grid to last longer and run cheaper in the end... such as putting power lines underground near the roads instead of cheaply on poles... higher voltage DC with local DC to AC with plenty of R&D available that no private company can compete with.
Like the roads, water, sewer grids before it, an open public electrical grid will foster competition built upon it and promote a distributed robust marketplace. Grid power storage services that buy cheap and sell high; small distributed power generation and a FAIR payback to individuals who feed to the grid. Many schemes could be devised on such systems, beyond just subsides for example, consumers could choose to pay more for solar and solar producers then get a higher payback. Power rates could be managed automatically down to the second; fostering a whole market of smart devices to save you money.
Power generation can remain private; just as cars, trucks are private but run on the public transportation grid. Although, I can't still see nuclear being possible without huge government intervention as has always been the case.
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